1. Field of the Invention
The present invention relates to boat hulls, and more particularly to a boat hull having a two-stage flow chamber in which the driving propeller is disposed.
2. Description of the Prior Art
It is well known in the prior art to provide a tunnel or propeller pocket in the hull of a boat to provide additional clearance between the bottom of the hull and the bottom of the waterway. In addition, it has been suggested that such tunnels tend to improve the efficiency of the propulsion system. Early patents, such as U.S. Pat. No. 128,407, have disclosed tunnels running the entire length of the hull which effectively forms a double hull. The use of pockets or cavities at the stern of the boat in which the propeller is mounted had been taught by the following U.S. Pat. Nos. 111,462; 3,515,087; 3,611,973; 4,371,350; and 4,383,828.
Generally, these patents teach a cavity or pocket which may extend for about one-third the length of the hull at the stern. A typical design is taught by the '087 and '973 patents both issued to Stuart. Stuart shows a U-shaped tunnel running aft to the amidship line of the hull toward the stern. The tunnel smoothly increases in size and diameter as it runs aft and is opened fully at the stern. Stuart claims an advantage in that the slipstream of water in the tunnel and aft of the propeller results in a jet-like stream of water producing a reaction drive similar to a jet engine.
I have found, however, that the Stuart design having a U-shaped cavity has a serious problem in that the water received by the propeller has been foiled off of the hull causing turbulence and cavitation. The result is poor performance of the propeller. Thus, there is a need for a hull tunnel design to provide the advantages of the low draft, yet which will not sacrifice efficiency due to turbulence and cavitation in the tunnel. I refer to such a design as a "flow chamber" since water will flow with a minimum of turbulence.